The present invention relates to a liquid-crystal composition and more particularly to a liquid-crystal composition for use in a multiplex-driving system in twisted nematic (TN) type liquid-crystal display devices.
In recent years, a larger information-content has been necessary in the field of liquid-crystal display devices. Accordingly, matrix displays are preferred to conventional segment displays. In a matrix display, the multiplexity (N) in the multiplex driving is increased to 32, 64, or more so as to further diversify the information content.
The drive of a liquid-crystal device of the X-Y matrix type by the optimized amplitude-selecting method of the multiplexity and the ratio .alpha. of the effective voltage Vrms (on) in the selected picture-element to the effective voltage Vrms (off) in the non-selected picture-element, is expressed by the well known formula: ##EQU1## As the N approaches .infin. in the formula, .alpha. becomes 1. As apparent from this formula, the ratio of Vrms(off) to Vrms(on) should be smaller as the multiplexity N increases. Accordingly, the matrix type liquid-crystal display devices having high information content require a liquid-crystal material to have sharp threshold characteristics, i.e., of superior contrast ratio provided by the small voltage ratio. The threshold characteristics of the conventional liquid-crystal material experienced problems such as low display contrast, narrow effective viewing-angle range, etc. caused when N became a value of 32 or higher.